The LEC team is focused on delivering an awesome Summer Split, Summer Finals, and preparing to host the 2019 World Championship in Europe. Since hosting Worlds 2019 is a big responsibility with a lot of work falling on the host region, the EU team requested for NA to host Rift Rivals again this year.
: https://eu.lolesports.com/en/articles/rift-rivals-2019-na-vs-eu